This invention relates generally to a holder or mount for a piezoelctric crystal used for determining electrical frequency, and more specifically relates to a holder for a piezoelectric quartz crystal wafer which securely supports the crystal wafer inside of a metal casing.
Electric filters are used, for example, to pass a band of electrical frequencies or to reject a band of electrical frequencies. When a filter requires a narrow bandwidth and/or a sharp cut off of the frequency response, a piezoelectric quartz crystal is usually utilized. Some of the areas crystal filters have wide application are: avionics communication and navigation, missiles, satellites, command destruct receivers, microwave telephone multiplex, amateur radio, military field radio, marine band radio, and broadcast and landmobile radio.
The holders or mounts for electrical crystals used prior to the invention herein generally comprised a base having a plurality of terminals, each connected to a point at the lower part of the crystal. This type of crystal holder is extensively used and is quite adequate in a low stress environment. However, under conditions of high shock and vibration, particularly when used in missile and satellite applications, for example, the crystals were subjected to severe stresses and were not sufficiently supported by the prior holder, and would often times short to the metallic outer casing or develope cracks in the body of the crystal.
Moreover, in the prior holders it was extremely difficult to maintain the distance substantially constant between the crystal and the outer metal casing. Hence, time consuming adjustment was required for varying the capacitance inorder to achieve the desired frequency response. By consistently positioning the crystal in the holder at substantially the same location, automation processes may be utilized for the inserting of the crystal in the holder, cementing the crystal to the holder and adjusting the crystal frequency.
The subject invention as more fully referred to below, overcomes the aforestated defects of prior crystal holders and provides a holder for piezoelectric crystals which supports the crystal under conditions of high stress. It also enables the crystal to be positioned at the same location with respect to the enclosure of the metallic outer casing, so that the capacitance between crystal and casing is maintained relatively constant. Therefore, the same circuit parameters could be used even at high frequencies, without adjustment, for reproducing the desired frequency response.